1. Field of the Invention
This invention relates to a drawing frame for a ring spinning apparatus, which drawing frame comprises two delivery rollers, which define between them an exit nip for a drawn fibrous roving and one of which defines on its air-permeable peripheral surface a deflecting path for the fibrous roving being delivered and a suction zone, which extends along the deflecting path between the exit nip and a pressure-applying roller, which is peripherally spaced from said nip, and said suction zone comprises two juxtaposed and laterally spaced apart branch suction zones, and a blast nozzle is disposed between said branch suction zones and is operable to direct an air blast against the suction-free area which is disposed between said branch suction zones, whereby the drawn fibrous roving is divided into two branch rovings.
2. Description of the Prior Art
It is desired to supply the ring spinning apparatus with a narrow drawn sliver which substantially conforms to the cross-section of the yarn which is to be made. For that purpose it is known from Austrian Patent Specification 391,328 to provide a suction zone on the air-permable peripheral surface of one of the two delivery rollers of the drawing frame downstream of the exit nip and to provide at least on one side of said suction zone a blast nozzle for directing an air blast transversely to the suction zone. When the drawn fibrous roving is held against a lateral displacement in the exit nip defined by the delivery rollers of the drawing frame and in a guiding gap which is defined by a succeeding pressure-applying roller the suction stream and the air blast cooperate to bundle the roving and to form a comparatively narrow sliver. The narrow sliver which leaves the guiding gap that is defined by the pressure-applying roller facilitates the twisting of the fibers by the revolving traveler of the ring spinning apparatus because there is no longer a need to converge laterally spaced apart fibers of a wider sliver in a distinctly triangular zone to form a roving which is circular in cross-section. The twisting conditions will be the more favorable the smaller is the size of that spinning triangle, particularly because the roving has only a very low strength at the spinning triangle in which the roving has not yet been twisted.
To eliminate the need for an expensive making of bundled rovings for ring spinning operations it is also known from Austrian Patent Specification 395 865 to divide a drawn roving into two branch rovings in an arrangement in which the suction zone on the periphery of one delivery roller of the drawing frame is divided into two laterally spaced apart branch suction zones and a blast nozzle is directed toward a suction-free area existing on the periphery of the delivery roller between said branch suction zones. As a result, the suction streams and the air blast cooperate to urge the fibers of the drawn roving apart and thus to form two branch rovings ant each branch roving will be bundled at the same time because the air blast has a distinct component of flow which is transverse to the branch rovings. This will result in a desirable decrease of the size of the spinning triangle which succeeds the guide gap defined between one delivery rollers and the pressure-applying roller adjacent to each branch roving.